Author: Dr Amanda Oakley MBChB FRACP, Dept of Dermatology Waikato Hospital, 2002.

What is a shampoo?

A shampoos is a cleanser designed to clean hair and scalp. Most shampoos clean hair very well. Where they differ is how the hair feels afterward, depending partly on the strength of the surfactants.

Ingredients of shampoo

All shampoos are 80–90% water, 2–8% detergents and foaming agents, and about 1% fragrance and preservatives.

Moisturizing shampoos are the best choice for dry, flyaway hair. They can cut down on static, make split ends look better (by gluing them together with proteins), and pull moisture onto hair to keep it from getting too dry.

How to use shampoo

Wet the scalp and hair using warm or cool water (hot water can be drying to the hair and scalp).

Lather is destroyed by sebum so an oily scalp may require a second shampoo. Excessive lather is wasteful: it doesn't clean hair any better. Shampoo should be easy to rinse off, but conditioner, styling products and chemical processes may leave a residue.

Conditioners are designed to counteract the effect of detergents, repair static electricity and split ends. A silicone film smoothes cuticles and reduces friction and hair breakage, and maintains colour. Conditioners often contain anionics for softness and manageability.

Medicated shampoo

Medicated shampoo may contain salicylic acid to loosen flakes of skin, and selenium sulfide, zinc pyrithione, ketoconazole or ciclopirox to reduce the numbers of Malassezia yeasts on the scalp and are used to treat dandruff and seborrhoeic dermatitis. They may also help treat scalp psoriasis and atopic dermatitis, but often shampoos containg coal tar are more useful in these conditions.

Medicated shampoo needs to be left on the scalp for longer than normal shampoo. Ideally, wet the hair 10 minutes before a shower or bath. Apply medicated shampoo as above. and massage gently into the scalp. Leave for 10 minutes and rinse off well. Follow with conditioner if desired.

Skin problems due to shampoo

Shampoos can irritate and cause scalp problems. These are rare with modern products made by reputable manufacturers if they have been designed for sensitive skin and are used appropriately. Overwashing may have the following effects:

Hypoallergenic products

The manufacturers of hypoallergenic shampoos have tried to avoid using substances that are likely to cause contact allergy. Their products are often "fragrance-free" (low levels of masking fragrances are permitted), "mild" and "non-irritating". If you have oily skin (seborrhoea), choose shampoo designed for your skin type.

A hypoallergenic product may still be irritating to those with very sensitive skin, and they may rarely cause contact allergy.

Labelling in the USA

For the US, the FDA states: "If a cosmetic claim is made on the label of a "true" soap or cleanser, such as moisturizing or deodorizing, the product must meet all FDA requirements for a cosmetic, and the label must list all ingredients. If a drug claim is made on a cleanser or soap, such as antibacterial, antiperspirant, or anti-acne, the product is a drug, and the label must list all active ingredients, as is required for all drug products."

There are no specific labelling requirements in New Zealand.

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